Electromagnetic horns

ABSTRACT

An electromagnetic horn comprises a casing, a resilient diaphragm closing the casing, an electromagnet carried by the casing, an armature associated with the electromagnet and secured to the diaphragm and a movable contact within the casing. The movable contact is movable into or out of engagement with the fixed contact by the armature to control energisation of the electromagnet and a bolt extends through the casing and is connected to the fixed contact so that rotation of the bolt relative to the fixed contact adjusts the position of the fixed contact relative to the casing. The head of the bolt is accessible from the exterior of the casing and is engaged in a restraining member which is secured to the casing so as to be immovable relative to the casing in a direction parallel to the axis of the bolt. The restraining member holds the bolt against axial movement relative to the casing but permits angular movement of the bolt relative to the casing.

United States Patent Parkes [15] 3,656,155 14 1 Apr. 11,1972

[54] ELECTROMAGNETIC HORNS [21] Appl. No: 30,869

[30] Foreign Application Priority Data secured to the diaphragm and a movable contact within the casing. The movable contact is movable into or out of engage- June 1 i, Great Bl'liall'l ..29,5 ment with the fixed ontact [he armature to control ener. gisation of the electromagnet and a bolt extends through the Cl 40/391 casing and is connected to the fixed contact so that rotation of [51 Int. Cl. ..G08b 3/00 the bolt relative to the fixed contact adjusts the position of the [58] Field of Search ..340/388, 39]; 151/69 fixed contact relative to the casing. The head of the bolt is accessible from the exterior of the casing and is engaged in a 5 Refe e Ci d restraining member which is secured to the casing so as to be immovable relative to the casing in a direction parallel to the, UNITED STATES PATENTS axis of the bolt. The restraining member holds the bolt against axial movement relative to the casing but permits angular 2,803,004 8/1957 White ..340/388 1,613,906 1/1927 Rohour 151/69 movement relat've the 63mg 3,510,922 5/1970 Dzus et all ..1'5l/69 6 Claims, 2 Drawing Figures FOREIGN PATENTS OR APPLICATIONS 558,456 6/1958 Canada ..l5l/69 Primary Examiner-Richard Murray Attorney-Holman, Glascock, Downing & Seebold [57] ABSTRACT An electromagnetic horn comprises a casing, a resilient diaphragm closing the casing, an electromagnet carried by the casing, an armature associated with the electromagnet and ELECTROMAGNETIC HORNS This invention relates to electromagnetic horns of'the kind comprising a casing, a resilient diaphragm closing the casing, an electromagnet carried by the casing, an armature associated with said electromagnet and secured to said diaphragm, a fixed contact and a movable contact within the casing, the movable contact being movable into or out of engagement with the fixed contact by the armature so as to control energisation of the electromagnet, and a bolt extending through the casing so as to be accessible from the exterior of the casing, and said bolt being connected to said fixed contact so that rotation of said bolt relative to the fixed contact adjusts the position of the fixed contact relative to the casing, and thereby adjusts the maximum gap which can occur between the fixed contact and the movable contact during operation of the horn.

According to the invention in a horn of the kind specified the head of said bolt is accessible from the exterior of the easing and is engaged in a member which is secured to the casing so as to be immovable relative to the casing in a direction parallel to the axis of the bolt, said member holding said bolt against axial movement relative to the casing but permitting angular movement of the bolt relative to the casing.

The invention further resides in a method of manufacturing an electromagnetic horn including the steps of engaging a stepped sleeve like member with a horn casing, so that a first portion of the sleeve of smaller diameter extends through a hole in the wall of the casing, and a second portion of the sleeve of larger diameter extends from the exterior surface of the casing, a shoulder defined at the junction of said portions of the sleeve engaging the exterior surface of the casing, deforming said first portion of the sleeve into engagement with the inner surface of the casing to secure the sleeve to the easing against movement in direction parallel to the axis of the sleeve, securing a sub-assembly including a fixed contact and a movable contact within the casing, inserting a bolt through said sleeve so that the head of the bolt engages in said second portion of the sleeve, coupling the shank of said bolt to the fixed contact so that rotation of the bolt adjusts the position of the fixed contact relative to the casing, and deforming said second portion of the sleeve, so as to prevent axial movement of the bolt relative to the casing while leaving the head of the bolt accessible to an operating tool.

One example of the invention is illustrated in the accompanyin g drawings wherein:

FIG. 1 is a section view of an electromagnetic horn, and

FIG. 2 is an enlarged view of part of FIG. 1.

Referring to the drawings, the horn includes a cylindrical metal casing 11 which is closed at one end by an integral base 12, and closed at its other end by a resilient diaphragm 13. The diaphragm 13 is in sealing engagement with a peripheral flange 11a of the casing 11. Secured to theinner surface of the base 12 is a hollow, cylindrical, synthetic resinformer 14having wound thereon the winding 15 of an electromagnet. Extending into the former 14 and in screw-threaded engagement with the walls of a plunged hole in the base 12 is a steel pole piece 16, the pole piece 16 projecting from the exterior of the base 12, and being slotted to receive a screw-driver, whereby the position of the pole piece, within the former, can be adjusted. Secured to the diaphragm 13, and extending into the former 14 towards the pole piece 16 is a cylindrical steel armature 17 which is formed intermediate its ends with a peripheral shoulder 18 upon which a fibre washer 19 seats.

Extending upwardly from the base 12 towards the diaphragm 13 is a support member 21 which carries a metal bridge piece 22 at its upper end. The metal bridge piece 22 extends adjacent the armature 17, generally parallel with the diaphragm l3, and at its end remote from the support member 21 the bridge piece 22 carries a moulded synthetic resin nut 23. Thrust between the bridge piece 22 and the former 14 is a conductive leaf spring 24, the leaf spring 24 being insulated from the bridge piece 22 and being electrically connected to one end of thewinding l5. Secured to the bridge piece 22, ad-

jacent the free end of the leaf spring 24 is a fixed contact 25, which is engageable by a movable contact 26 secured to the leaf spring 24. The leaf spring 24 includes an integral tag (not shown) which is engageable by the fibre washer 19 on the armature 17, and the leaf spring 24 is such that it urges the movable contact 26 into engagement with the fixed contact 25. The fixed contact 25 is electrically connected through the bridging piece 22 and the support member 21 to a first terminal on the exterior of the casing, and the end of the winding 18, remote from the leaf spring 24, is electrically connected to a second terminal on the exterior of the casing.

Extending through an aperture in the base 12 of the casing 11 is a bolt 27, the threadedshank of which is engaged with the nut 23, and the head of which is engaged in a metal restraining member 28 on the exterior of the base 12. The member 28 is in the form of a metal sleeve having an outwardly directed peripheral flange 29 which engages the inner surface of the base 12, and a cup-like portion 31 which partially surrounds the head of the bolt 27 and which engages the outer surface of the base 12. The portions 29, 31 of the member 28 are inter-connected by an integral neck which extends through the aperture in the base 12, and the member 28 holds the bolt 27 against axial movement relative to the casing 11 while permitting angular movement of the bolt 27 relative to the casing. The portion 31 of the member 28 does not totally enclose the head of the bolt 27, but leaves the portion ,of the head which is engageable by a screwdriver clear.

In use, the two terminals on the exterior of the casing are electrically connected to respective poles of do supply, and the contacts 25, 26 are normally closed. Thus, current flows in the winding 15 thereby energising the electromagnet defined by the winding 15 and the pole 16, whereupon the armature 17 is attracted towards the pole 16 and moves towards the pole 16 as permitted by deformation of the diaphragm 13. As the armature 17 moves towards the pole 16 the fibre washer 19 engages said tongue of the leaf spring 24 and flexes the leaf spring 24 in a direction to move the contact 26 out of engagement with the contact 25. As soonas the contacts 26, 25 open, the circuit through the winding 15 is broken, and so the electromagnet is de-energised and the armature 17 moves in the opposite direction under the action of the inherent resilience of the diaphragm 13, thereby permitting the contacts 25, 26 to close again so that the cycle is repeated. Thus, as long as the dc. supply is maintained across the external terminals the armature 17 will be caused to reciprocate back and forth, and the diaphragm 13 will be vibrated and will generate sound.

The horn is assembled in the following manner. The winding 15 is wound onto the former l4, and the ends of the windings are secured to metal tags carried by the former. The nut 23 and the contact 25 are secured to the bridging member 22, and the bridging member 22 and the support member 21 are riveted to the former 14, with one end of the leaf spring 24 trapped between the former and the bridging member 22. The contact 26 is at this stage already secured to the other end of the leaf spring 24, and the leaf spring 24 is spaced from the bridging piece 22 by a synthetic resin. washer so that the leaf spring 24 is insulated from the bridge piece 22. The connection between said one end of the winding 15 and the leaf spring 24 is made by trapping said metal strip, which is secured to the one end of the winding, between the former and the leaf spring 24, a single rivet being used to secure the bridge piece 22, the synthetic resin washer, and the leaf spring 24 to the former. The stepped metal sleeve, which will subsequently define the member 28 is then engaged with the casing 11 by inserting the portion of smaller diameter through a previously formed aperture in the base 12, so that the shoulder defined between the two portions of the sleeve engages the outer surface of the base 12. The free end of the portion of smaller diameter is then deformed to define the flange 29 engaging the inner surface of the base 12, thereby securing the sleeveto the base 12. a

The assembly including the support member 21, the bridge piece 22 and the former 14 is then inserted into the casing,

and is riveted into position. One of the rivets securing the said assembly to the casing extends through part of the support member 21, through part of the former 14, through an insulating block engaged with the outer surface of the base 12, and through a first terminal blade carried by the insulating block, the rivet serving to electrically interconnect the support member 21 and the first terminal blade. A second rivet securing the said assembly in the casing extends through the conductive strip which is electrically connected to said other end of the winding 15, through a further part of the former 14, through the base 12, through said insulating block and through a second terminal blade carried by the insulating block, the rivet serving to electrically interconnect the conductive strip and the second terminal blade. Thus, when the contacts 25, 26 are inter-engaged then the first and second terminal blades are electrically connected to the support member 21, the bridge piece 22, the contacts 25, 26, the conductive leaf spring 24, and the winding 15.

The diaphragm 13 carrying the armature 17 is then riveted to the flange 11a of the casing to close the casing, a sealing gasket being trapped between the diaphragm 13 and the flange 11a, and the pole piece 16 is screwed into a central, plunged hole in the base 12, so that the pole piece 16 extends towards the armature 17 within the former 14. The bolt 27 which is of the pan head type is then inserted through the sleeve, and the corresponding hole in the former 14 and the free end of the shank of the bolt 27 is engaged in the moulded synthetic resin nut 23. The head of the bolt 27 engages in the portion of the sleeve of larger diameter, is then deformed to constitute the portion 31 trapping the head of the bolt 27. The deformation of the portion of the sleeve of larger diameter is such that a cruciform groove in the head of the bolt 27 is left exposed so as to be accessible by a screwdriver.

The first and second terminals are then connected to respective poles of a dc. supply, and the horn is energised. The pole piece 16 is then screwed in or out until the tone produced by the horn is approximately the desired tone. The movement of the pole is a relatively coarse adjustment of the tuning of the horn, and in order to finally tune the born the bolt 27 is rotated. Since the bolt 27 is held by the member 28 against axial movement, the rotation of the bolt causes movement of the nut 23 in a direction parallel to the axis of the bolt 27, and thereby flexes the bridge member 22 in a direction to move the fixed contact towards or away from the movable contact 26. The bolt 27 is rotated in this manner until the tone produced by the horn is that which is desired. It will be appreciated, that since the contact 26 is urged by the spring 24 into engagement with the contact 25 then unless the tongue of the spring 24 is engaged with the fibre washer 18 on the armature 17 then during movement of the contact 25 the contact 26 will remain in engagement with the contact 25 and will move with the contact 25. However, the movement of the contact 25 adjusts the maximum gap which can occur between the contact 25,26 when the horn is operating, since the contact 25 is moved relative to the stable position of the armature 17.

When the horn has been tuned to produce a desired tone the exterior of the horn is coated with paint and is then stoved. During the coating of the horn with paint the paint enters the member 28, and so when the paint has been stoved, the bolt 27 is effectively locked to the member 28 by the layer of stoved paint. The nut 23 is split, and is such that it grips the shank of the bolt 27, and thereby acts as its own lock nut to resist rotation of the bolt 27, relative to the nut 23, during operation of the horn due to the vibration of the horn. Moreover, the former 14 includes an internal annular collar through which the pole piece 16 extends, the collar of the former l4 gripping the pole piece 16 and acting as a lock nut to retain the pole 16 in the preset position.

1n a modification the member 28 rotates with the bolt 27,

the former l4 gripping the flange 29 of the member 28 sufficiently tightly to prevent rotation of the bolt 27 and member 28 due to vibration during tuning of the horn, and the final painting of the horn locking the bolt 27 and the member 28 to one another and to the casing 11.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. An improved electromagnetic horn of the kind comprising a hollow casing, a resilient diaphragm closing the casing, an electromagnet carried by the casing, an armature associated with said electromagnet and secured to the diaphragm, a fixed contact and a movable contact within the casing, the movable contact being movable into and out of engagement with the fixed contact by the armature so as to control energisation of the electromagnet, and a bolt extending through the casing so as to be accessible from the exterior of the casing, said bolts being connected to said fixed contact so that rotation of the bolt relative to the fixed contact adjusts the position of the fixed contact relative to the casing and thereby adjusts the maximum gap which can occur between the fixed contact and the movable contact during operation of the horn, wherein the improvement comprises, the head of said bolt is accessible from the exterior of the casing and is engaged in a member which is secured to the casing so as to be immovable relative to the casing in a direction parallel to the axis of the bolt, said member holding said bolt against axial movement relative to the casing but permitting angular movement of the bolt relative to the casing.

2. A horn as claimed in claim 1 wherein the free end of the shank of said bolt is engaged in a nut carried by said fixed contact, said nut being split and being arranged to grip theshank of the bolt so that rotation of the bolt relative to the nut owing to vibration of the horn in use is prevented.

3. A horn as claimed in claim 1 wherein said member includes an integral, outwardly directed flange and an integral, substantially cup-shaped portion, said flange and said cupshaped portion trapping the casing therebetween and the head of said bolt being engaged in said cup-shaped portion.

4. A horn as claimed in claim 1 wherein both said member and said bolt can move angularly relative to the casing, while turning the horn during manufacture thereof.

5. A method of manufacturing an electromagnetic horn including the steps of engaging a stepped sleeve like member with a horn casing, so that a first portion of the sleeve of smaller diameter extends through a hole in the wall of the casing, and a second portion of the sleeve of larger diameter extends from the exterior surface of the casing, a shoulder defined at the junction of said portions of the sleeve engaging the exterior surface of the casing, deforming said first portion of the sleeve into engagement with the inner surface of the casing to secure the sleeve to the casing against movement in direction parallel to the axis of the sleeve, securing a sub-assembly including a fixed contact and a movable contact within the casing, inserting a bolt through said sleeve so that the head of the bolt engages in said second portion of the sleeve, coupling the shank of said bolt to the fixed contact so that rotation of the bolt adjusts the position of the fixed contact relative to the casing, and deforming said second portion of the sleeve, so as to prevent axial movement of the bolt relative to the casing while leaving the head of the bolt accessible to an operating tool.

6. A method as claimed in claim 5 including the further steps of tuning the assembled born to produce the required tone, coating the exterior of the casing of the horn with paint, the arrangement being such that paint is provided between the second portion of the sleeve and the head of said bolt, and stoving the paint to produce the required finish and to lock the bolt in position in said sleeve. 

1. An improved electromagnetic horn of the kind comprising a hollow casing, a resilient diaphragm closing the casing, an electromagnet carried by the casing, an armature associated with said electromagnet and secured to the diaphragm, a fixed contact and a movable contact within the casing, the movable contact being movable into and out of engagement with the fixed contact by the armature so as to control energisation of the electromagnet, and a bolt extending through the casing so as to be accessible from the exterior of the casing, said bolts being connected to said fixed contact so that rotation of the bolt relative to the fixed contact adjusts the position of the fixed contact relative to the casing and thereby adjusts the maximum gap which can occur between the fixed contact and the movable contact during operation of the horn, wherein the improvement comprises, the head of said bolt is accessible from the exterior of the casing and is engaged in a member which is secured to the casing so as to be immovable relative to the casing in a direction parallel to the axis of the bolt, said member holding said bolt against axial movement relative to the casing but permitting angular movement of the bolt relative to the casing.
 2. A horn as claimed in claim 1 wherein the free end of the shank of said bolt is engaged in a nut carried by said fixed contact, said nut being split and being arranged to grip the shank of the bolt so that rotation of the bolt relative to the nut owing to vibration of the horn in use is prevented.
 3. A horn as claimed in claim 1 wherein said member includes an integral, outwardly directed flange and an integral, substantially cup-shaped portion, said flange and said cup-shaped portion trapping the casing therebetween and the head of said bolt being engaged in said cup-shaped portion.
 4. A horn as claimed in claim 1 wherein both said member and said bolt can move angularly relative to the casing, while turning the horn during manufacture thereof.
 5. A method of manufacturing an electromagnetic horn including the steps of engaging a stepped sleeve like member with a horn casing, so that a first portion of the sleeve of smaller diameter extends through a hole in the wall of the casing, and a second portion of the sleeve of larger diameter extends from the exterior surface of the casing, a shoulder defined at the junction of said portions of the sleeve engaging the exterior surface of the casing, deforming said first portion of the sleeve into engagement with the inner surface of the casing to secure the sleeve to the casing against movement in direction parallel to the axis of the sleeve, securing a sub-assembly including a fixed contact and a movable contact within the casing, inserting a bolt through said sleeve so that the head of the bolt engages in said second portion of the sleeve, coupling the shank of said bolt to the fixed contact so that rotation of the bolt adjusts the position of the fixed contact relative to the casing, and deforming said second portion of the sleeve, so as to prevent axial movement of the bolt relative to the casing while leaving the head of the bolt accessible to an operating tool.
 6. A method as claimed in claim 5 including the further steps of tuning the assembled horn to produce the required tone, coating the exterior of the casing of the horn with paint, the arrangement being such that paint is provided between the second portion of the sleeve and the head of said bolt, and stoving the paint to produce the required finish and to lock the bolt in position in said sleeve. 